Metal Mold, and Formed Body Molding Method by the Metal Mold

ABSTRACT

A metal mold capable of preventing a nonuniform wall thickness from occurring in a cylindrical formed product, wherein a gate ( 8 ) for filling molding material is formed in alignment with the center axis (CL) of a tubular mold cavity ( 4 ) so that metered resin can be injected and filled from the tip side of a core ( 5 ) into the mold cavity, whereby since the metered molding material injected from the gate into the mold cavity uniformly flows around the core, a force is uniformly applied to the side face of the core through all the periphery thereof to prevent the core from falling in one direction and to always position the core at the center of the mold cavity, the molded formed product cannot cause the nonuniform wall thickness.

TECHNICAL FIELD

The present invention relates to a resource-saving type metal mold and aformed body molding method of a mold using the metal mold, which iscapable of molding, in a case of a cylindrical molding, without causingnonuniform wall thickness using a molding material such as a resin, akneaded material of a sintering powder and a resin binder or the like,and suitable for molding a molded formed product such as a cylinder fora syringe which requires an extremely high cleanliness and precision.

BACKGROUND ART

In a conventional metal mold (101) for cylinder molding, as shown inFIG. 7, a hot runner (107) is disposed in the central area of a femaledie (102) and a cold runner (108) is formed perpendicular thereto, and ametered resin (109) is filled within a cavity (106) with a high pressurethrough a flange portion (110 c) of a cylinder (110). In this method,when the metered resin (109) is injected into the cavity (106) with ahigh pressure through the flange portion (110 c) of the cylinder (110),the metered resin (109) is gradually filled therein from a portioncloser to the gate (111) of the flange portion (110 c) as shown in FIG.8.

The injection filling pressure to the metered resin (109) reaches to ahigh pressure of 1,000-2,000 kg/cm², and a force (F) perpendicular tothe center axis (CL) of the core (105) is applied to the side faceportion of the core (105) closer to the gate (111), from which the resin(109) is filled first, a slight sag is made on the core (105) in adirection away from the gate (111). When, such sag is generated, adifference [(t1)>(t2)] is generated between the width at the gate side(t1) and the width at the opposite side (t2) of the cavity (106), whichis formed by the core (105) and the mold cavity (104) formed in thefemale die (102), a nonuniform wall thickness is generated in the moldedcylinder (110) (U.S. Pat. No. 6,562,009B1).

An object of the present invention is to provide a hot runner type metalmold, which does not cause nonuniform wall thickness unlike the coldrunner type which causes nonuniform wall thickness, and a formed bodymolding method using the metal mold.

DISCLOSURE OF THE INVENTION

An aspect of a metal mold (1) according to claim 1 of the presentinvention is a metal mold (1), which includes:

a cavity (6) having a predetermined internal shape;

a molding material injection path (12) communicated with the cavity (6)via a gate (8) for supplying a metered fluid molding material (9) to thecavity (6); and

a valve pin (7) disposed within the molding material injection path (12)so as to be inserted into and pulled out from the gate (8),

wherein the cavity (6) is formed with a cylindrical mold cavity (4) anda columnar core (5) to be coaxially inserted into and pulled out fromthe mold cavity (4), and the gate (8) for injecting the molding materialis formed in alignment with the center axis (CL) of the mold cavity (4)to inject a metered resin from the front end side of the core (5) andfill the core (5) therewith. Accordingly, the gate (8) is formed on thecenter axis (CL) of the mold cavity (4) and the core (5), the meteredmolding material (9) injected into the cavity (6) from the gate (8)flows uniformly around the periphery of the core (5); no force isapplied to the side face of the core (5) from one direction; the core(5) is prevented from falling in one direction but always positioned atthe center of the mold cavity (4) throughout the course of the injectionand filling of the molding material; as a result, a nonuniform wallthickness is not generated in the molded formed product (10).

As a particular shape of the cavity (6), there may be given such anexample that the mold cavity (4) forms the outer surface of thecylinder, and the core (5) is for forming the cylinder inner surface.

As for the molding material (9) in the present invention, in addition toordinary resins, a kneaded material of a sintering powder and a resinbinder may be used.

A molding method using the metal mold (1) is a formed body moldingmethod, which includes the steps of:

(a) injecting a metered molding material (9) from the molding materialsupply side (12) into a cavity (6) via a gate (8) to fill the cavity (6)therewith,

(b) after filling the cavity, applying and maintaining a predeterminedpressure to the filled material within the cavity,

(c) after completing the pressure applying and maintaining step andafter gate cutoff, returning a surplus molding material (9 a) remainingat the gate (8) portion to the molding material supply side (12), and

(d) cooling the molding material (9) within the cavity (6) to solidifyinto a formed body (10), and then taking out the formed body (10),

wherein the cavity (6) includes a cylindrical mold cavity (4) and acolumnar core (5) to be coaxially inserted into and pulled out from themold cavity (4), and the gate (8) for injecting the molding material isformed in alignment with the center axis (CL) of the mold cavity (4), ametered resin is injected from the front end side of the core (5) tofill the core therewith.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view showing a state of a closed metal moldaccording to a first embodiment of the present invention,

FIG. 2 is a cross sectional view showing a state of gate-cut performedby the valve pin in FIG. 1,

FIG. 3 is a cross sectional view showing a state that the metal mold inaccordance with the first embodiment of the present invention is opened,

FIG. 4 is a cross sectional view showing a state that products areejected from the metal mold in accordance with the first embodiment ofthe present invention,

FIG. 5 is an enlarged cross sectional view of a gate-cut state in themetal mold in accordance with the first embodiment of the presentinvention,

FIG. 6 is an enlarged cross sectional view of a gate-open state in themetal mold in accordance with the first embodiment of the presentinvention,

FIG. 7 is a cross sectional view of a conventional example, and

FIG. 8 is an enlarged cross sectional view showing a state where meteredmolding material is being filled in the conventional example.

CL BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail inaccordance with an embodiment with reference to the drawings. Thepresent invention is applicable to forming any runner-less cylinder. Asa typical example of the embodiment, a case where a cylindrical moldedformed product (10) is produced using a columnar core (5) and acylindrical mold cavity (4) will be described. The description will bemade mainly taking an example in which an ordinary resin is used as amolding material. Other materials such as a kneaded material of asintering powder and a resin binder may be used; and the followingmaterials are available.

The molding material (9) includes a sintering powder and a binder resinincluding mainly two kinds of resins constituting a uniform mixture of asolvent soluble resin and a solvent insoluble resin. The sinteringpowder includes a metal material, an oxide, a nitride, quartz or glassas a main material to be sintered and a binder for binding the above.

As for the main sintering materials capable of being sintered, metalmaterials (stainless powder, Ni, W, Mo, Fe), carbides (WC, TiC, chromiumcarbide), nitrides (boron nitride, silicon nitride, aluminum nitride),oxides (quartz, aluminum, glass, zirconium) are available; and as thebinder for binding these main sintering materials, Co and Ni areavailable. The oxides (quartz, aluminum, glass, zirconium) may besintered with no binder. As the sintering articles of these materials,carbide material, cermet material, ceramic material, quartz glassmaterial, tungsten material, stainless material, nickel material,molybdenum material, glass material or compound materials of the aboveare available. The optimum average particle size of the main sinteringmaterial depends on the usage. For example, in the case of the carbidematerial, average particle size of 0.2-0.5 μm or so is preferred forensuring the durability of the edge portion. Ordinary average particlesize is 2 μm or so.

The binder resin for supporting the sintering powder includes a solventsoluble resin, which is solved into one solvent and solvent insolubleresin, which is not solved into the solvent, as the main material andnecessary additives such as plasticizer and release agent. It ispreferred that the solvent soluble resin and the solvent insoluble resinare completely mixed and coexisting with each other at operationtemperature. In this embodiment, the following resin is used; i.e., bothare solved into a solvent at a melting temperature (high temperature)and separated from each other in a state that both are uniformly mixedwith each other at an operation temperature.

Further, in order to enhance the shape retaining performance afterdegreasing and the uniform dispersion of the sintering powder, it ispreferred to use a resin, which becomes fibrous or plumose in thesolvent insoluble resin, rather than the case where the solvent solubleresin and the solvent insoluble resin are simply mixed. That is, in thecase of a resin in which the solvent insoluble resin becomes fibrous orplumose, both are completely solved into the solvent soluble resin at ahigh temperature (=melting temperature of both). When the above iscooled down, the solvent insoluble resin is gradually separated out in afibrous state; and among the fibers, the solvent soluble resin and thesintering powder are left in an entwined state; thus the solvent solubleresin and the sintering powder are extremely finely and uniformlydispersed into the fibrous solvent insoluble resin.

As an example of such solvent soluble resins, polystyrene, acrylateresin, vinyl chloride, cyclic polyolefin resin, polycarbonate andtransient plastic are available. As an example of the solvent insolubleresin, polypropylene, polyethylene, polyacetal and the like areavailable. As for the solvent for solving the above at a hightemperature (solvent insoluble resin separates at a room temperature),for example, aromatic solvents such as xylene, toluene, benzene andchlorinated solvents such as dichloromethane and dichloroethane areavailable. Further, as a plasticizer, dioctylphthalate, dibutylphthalateor the like are available. As a release agent, zinc stearate, stearicacid amide are available. The mixture ratio between the solventinsoluble resin and the solvent soluble resin is 1:0.5-4.0 in volumeratio. The volume ratio between the binder resin and the sinteringpowder is 40:60-65:35. The above materials are formed into an ordinarypellet state and used in the same manner as the ordinary resin.

Now, descriptions will be made with reference to FIGS. 1-6. A metal mold(1) comprises a female die (2) and a male die (3), and the female die(2) and the male die (3) are attached to a fixed die plate (15) and amoving die plate (16) respectively. The male die (3) is arranged so asto open and close with respect to the female die (2) (as a matter ofcourse, although not shown in the figures, a relationship therebetweenmay be opposite to the above).

The female die (2) includes a first female member (2 a) having a partingface (P2), a cavity member (30) formed with the mold cavity (4) andattached to the first female member (2 a), a second female member (2 b)formed in the rear side of the first female member (2 a), a pin drivesection (25), which is hydraulically or pneumatically driven for movingvalve pins (7) forward/backward via a hot runner bush (20) and a valvepin operation rod (25 a) and attached to the second female member (2 b),a sprue-mounting block (27) attached to the rear side of the secondfemale member (2 b), a third female member (2 d) constituting the rearside of the female die (2) for fixing the female die (2) to the fixeddie plate (15), a spacer member (2 c) disposed between the second femalemember (2 b) and the third female member (2 d) for forming a housingspace (28) for the sprue-mounting block (27) between the members (2 b)and (2 d), auxiliary springs (25 d) disposed between the third femalemember (2 d) and the valve pin operation rod (25 a) for pressurizing thevalve pins (7) in the gate-cut direction to urge the gate-cut operationof the pin drive section (25), and the valve pins (7).

The first female member (2 a) is formed with one or a plurality ofrecess (18) from the parting face (P2) thereof to the rear face, and therecess (18) receives the cavity member (30) formed with the mold cavity(4) having the opening at the parting face (P2) side. Here, the recessof the mold cavity (4) is formed in accordance with the outer peripheryshape of the cylinder (10′).

The mold cavity (4) of the cavity member (30) will be described indetail with reference to FIGS. 5 and 6. In the portion where the cavitymember (30) faces to the hot runner bush (20), a thin gate (8), whichcommunicates with the molding material injection path (12) of the hotrunner bush (20), is formed. Being continued to the gate (8), an outerperiphery portion of a thin front-end portion (10 a) of the cylinder(10′), to which a needle for a syringe having a diameter slightly largerthan the gate (8) is attached, is formed. And further, being continuedto the thin front-end portion (10 a), the outer periphery portion of thecylinder body (10 b) is formed. The outer periphery portion of a flangeportion (10 c) having the largest diameter is formed in the parting faceside.

As shown in the enlarged view of the gate portion in FIG. 5, a portion(8 a) from the thin front end portion (10 a) toward the rear direction[molding material supply side (1)] in the gate (8) is formed in astraight cylindrical shape; and a horn-like portion (8 b) is formed in ahorn-like shape being widely opened toward the rear direction from thecylindrical portion (8 a). And it is arranged so that the front-endportion of the valve pin (7), which will be described later, isprecisely engaged with the portion of the gate (8). And it is arrangedso that the front-end portion of the valve pin (7), which will bedescribed later, is inserted into and pulled out from the gate (8) toopen/close the gate (8).

In the hot runner bush (20), the molding material injection path (12),which is inserted with the valve pin (7) and is connected to the moldingmaterial communicating path (24), is formed; the front-end portionthereof is connected to the gate (8), and is formed being tapered thesame as that of the horn-like portion (8 b) of the gate (8). In the hotrunner bush (20), for example, a heater (29) is disposed to heat themolding material (9) within the molding material injection path (12) ofthe hot runner bush (20) up to the gate (8) to keep the molten statethereof. Reference numeral (19) denotes a receiving hole for the hotrunner bush (20).

As described above, the sprue-mounting block (27) is attached with asprue bush (22); and being communicated with the sprue bush (22), one orplurality of the molding material communicating paths (24), which isbranched on its way and connected to the molding material injectionpaths (12), are formed through the sprue bush (22) and thesprue-mounting block (27). Further, guide holes (21) for guiding thevalve pins (7), which will be described later, are formed in thesprue-mounting block (27).

The valve pin (7) is a member having a rod-like shape of which the frontend portion is formed in a tapered shape, and the rear end thereof isfixed to the valve pin operation rod (25 a). The valve pin (7) isslidably inserted through the guide hole (21), and the portionprotruding from the sprue-mounting block (27) is inserted into themolding material injection path (12) of the hot runner bush (20). Thefront-end portion of the valve pin (7) is formed so as to preciselyengaged with the gate (8). That is, as shown in the enlarged crosssectional view in FIG. 6, the front-end portion of the valve pin (7)includes a portion (7 a), which straightly extends from the cavity sideend (11) toward the rear direction in accordance with the cylindricalportion (8 a) of the gate (8), and a tapered portion (7 b) of which thediameter increases gradually toward the rear direction from thestraightly extending portion (7 a). The taper angle of the taperedportion (7 b) is slightly smaller and obtuse than that of the horn-likeportion (8 b). Accordingly, when the front-end portion is inserted intothe gate (8), the front end portion is guided by the horn-like portion(8 b), and the straightly extending portion (7 a) of the front endportion perfectly fits with the cylindrical portion (8 a) of the gate(8); thereby the gate-cut is reliably performed. In other words, thestraightly extending portion (7 a) and the cylindrical portion (8 a) ofthe gate (8) are molded so that the diameter and the inner diameterthereof fit with each other with nearly zero error.

Further, on the cavity side end (11), a circular cone recess (7 c) isformed so that circular cone-like portion (5 e) on the front end of thecore (5), which will be described later, precisely fits therewith. Thediameter (d) of the circular cone recess (7 c) on the cavity side end(11) is formed so as to be identical to the maximum diameter (d) of thecircular cone-like portion (5 e) on the front end of the core (5), butsmaller than the inner diameter (D) of the cylindrical portion (8 a).Accordingly, a gap (K) is formed between the cylindrical portion (8 a)and the circular cone-like portion (5 e) as shown in FIG. 5. When thefront-end portion of the valve pin (7) is separated away from the gate(8), the molding material (9) flows into the cavity (6) through the gap(K) as shown in FIG. 5. On the other hand, when the front-end portion ofthe valve pin (7) is engaged with the gate (8), the gap (K) is closed bythe front ring portion (11 a) of the cavity side end (11). As a matterof course, at this time, since the straightly extending portion (7 a) isfitted with the cylindrical portion (8 a) of the gate (8) with no gap,the molding material (9) does not enter into the cylindrical portion (8a). The front ring portion (11 a) means a plane ring face between theperiphery of the cavity side end (11) and the maximum inner diameter ofthe circular cone recess (7 c).

Further, in the front-end portion of the valve pin (7), a front-endnarrow hole (13 a), which is drilled from the head portion in the axialdirection of the circular cone recess (7 c), and a perpendicular narrowhole (13 b), which is perpendicular thereto and communicates thefront-end narrow hole (13 a) and the outer surfaces of the valve pin(7), are formed; and the front-end narrow hole (13 a) and theperpendicular narrow hole (13 b) forms a communicating hole (13).

The pin drive section (25) includes cylinder holes (25 b) formed in thesecond female member (2 b) and piston members (25 c), and the valve pinoperation rods (25 a) are bridged onto the piston members (25 c). Byactivating the piston members (25 c), the valve pins (7) are driven toslide via the valve pin operation rods (25 a). Reference symbols (M) and(N) denote outlets and inlets of the compressed oil/air for activatingthe piston members (25 c). Owing to the working of the auxiliary springs(25 d), the dimensions of the pin drive section (25) can be reduced, andthereby the entire sizes of the metal mold (1) can be reduced.

The male die (3) includes a male die body (3 a) attached to the movingdie plate (16), one or a plurality of cores (5) attached inside of themale die body (3 a) in alignment with the die cavities (4) and anintermediate die (3 b), which is disposed so as to be brought intocontact with and parted from the inside of the male die body (3 a) andthe core (5) is inserted thereinto and pulled out therefrom, andpush-out members (26) that, after the metal mold is opened, pushes theintermediate die (3 b) in the separating direction to separate themolded cylinders (10′).

An embedded end portion (5 d) of the core (5) is embedded in the maledie body (3 a), and the core (5) includes a base portion (5 c)protruding from the inside of the male die body (3 a), a columnarportion (5 b), which has the same shape as the inner peripheral shape ofthe cylindrical portion of the mold cavity (4) in the front end sidefrom the base portion (5 c) and forms the inner shape of the flangeportion (10 c) of the cylinder (10′) and the cylinder portion (10 b),and a projecting portion (5 a) formed being projected in the center ofthe front end of the columnar portion (5 b) to form the inner peripherysurface of the needle mounting portion (10 a) of the cylinder (10′). Thefront-end portion of the projecting portion (5 a) has a circularcone-like shape as described above, and the diameter of the circularcone-like portion (5 e) is (d).

The operation of the metal mold (1) according to the present inventionwill be described below. First of all, the moving die plate (16) isactivated to press the male die (3) onto the female die (2) and moldthem. At this time, the state where the gate (8) is closed by thefront-end portion of the valve pin (7) and the circular cone-likeportion (5 e) at the front end of the core (5) is closely fitted withthe circular cone recess (7 c) of the valve pin (7) is obtained as shownin FIG. 1.

Then, the pin drive section (25) is activated to pull out the valve pin(7) to open the gate (8) as shown in FIG. 2. In this state, aninjection-molding machine is activated and the metered molding material(9) is injected through a nozzle (23). The metered molding material (9)is injected into the cavity (6) through the gate (8) via the sprue bush(22), the molding material communicating path (24) and the moldingmaterial injection path (12) being applied with a high pressure (forexample, 1,000-2,000 kg/cm²). The state at this time is illustrated indetail in the enlarged drawing in FIG. 5.

As illustrated in FIG. 5, since the gate (8) is formed on the centeraxis (CL) of the core (5), the gap (K) formed by the cylindrical portion(8 a) of the gate (8) and the projecting portion (5 a) of the core (5)is formed with an identical width [(D-d)/2] all around the peripherythereof. Therefore, the metered molding material (9), which flows intothe cavity (6) through the gate (8) being applied with a high pressure,flows into cavity (6) uniformly all around the periphery thereof.Accordingly, the force is applied uniformly onto the outer periphery ofthe core (5). Unlike the conventional manner, the core (5) is not saggedto be inclined in one direction. Therefore, the cavity (6) does notgenerate nonuniform wall thickness from the beginning to the end of theinjection molding; and accordingly, nonuniform wall thickness is notgenerated in the thickness of the molded cylinder (10′).

When the cavity (6) has been filled with the metered molding material(9) as described above, the pressure applying and maintaining stepstarts to continuously apply a pressure to the filled molding material(9) within the cavity (6) from the nozzle (23) of the injection moldingmachine. When being cooled down, although the filled molding material(9) gradually solidifies and simultaneously deflates, owing to thepressure, the molding material (9) is replenished from the gate (8); andthus, the cylinder (10′) is prevented from sagging due to the pressureabove. When the cylinder (10′) is cooled down to a certain level and nodeflation is caused, the pressure applying and maintaining step isterminated, the pin drive section (25) is activated to reverse to makethe valve pin (7) advance; thereby the gate (8) is closed with thefront-end portion of the valve pin (7) as illustrated in detail in theenlarged view in FIG. 6.

At this time, in the gate (8) portion, the surplus molding material (9a) caught between the cavity side end (11) of the valve pin (7) and thefront end (14) of the core (5) can escape to the molding materialinjection path (12) through the communicating hole (13). Therefore, thecircular cone-like portion (5 e) at the front end of the valve pin (7)is closely fitted with circular cone recess (7 c) on the cavity side end(11) of the valve pin (7) to close the front-end narrow hole (13 a).Further, the straightly extending portion (7 a) of the valve pin (7)engages with the cylindrical portion (8 a) of the gate (8) with noclearance to close the gate (8). Thus, the gap (K) is closed by thefront ring portion (11 a) of the periphery portion on the cavity sideend (11) of the valve pin (7); and the gate-cut is reliably performedwith a small force. Accordingly, the cavity (6) is reliably blocked offfrom the molding material injection path (12).

Through the following cooling step, the filled molding material (9)within the cavity (6) is gradually cooled down and solidified. When themolding material (9) has been solidified, the moving die plate (16) isactivated to separate the male die (3) from the female die (2) to openthe metal mold as shown in FIG. 3. The molded formed product (10) ispulled out form the mold cavity (4) of the female die (2) being mountedon the core (5).

At this time, as illustrated in detail in the enlarged view in FIG. 6,the front end of the needle mounting portion (10 a) of the cylinder(10′) is completely blocked off from the molding material injection path(12). However, since the molding material (9) within the moldingmaterial injection path (12) is maintained in a molten state by the hotrunner bush (20), the cylinder (10′) as the molded formed product istaken out from the mold cavity (4) in a completely molded state, unlikethe conventional manner, free from a cold runner. Therefore, the coldrunner, which is conventionally disposed of uselessly, is not generated.

Last, the push-out member (26) is activated to separate the intermediatedie (3 b) from the male die body (3 a); the cylinder (10′) is pushed outbeing engaged with the flange portion (10 c) thereof to separate thecylinder (10′) from the core (5). After taking out the cylinder (10′),the parting face is cleaned, and the metal mold is molded to repeat theabove-described steps.

INDUSTRIAL APPLICABILITY

As described above, according to the present invention, since the gateis formed on the center axis of the core, the metered molding materialinjected into the cavity from the gate flows uniformly around theperipheral surface of the core. Therefore, since the force is uniformlyapplied to the side face of the core all around the peripheral surfacethereof, the core is prevented from falling in one direction but alwayspositioned at the center of the mold cavity. Accordingly, the moldedformed product is free from the nonuniformwall thickness.

1. (canceled)
 2. A metal mold, comprising: a cavity having apredetermined internal shape; a molding material injection pathcommunicated with the cavity via a gate for supplying a metered fluidmolding material to the cavity; and a valve pin disposed within themolding material injection path so as to be inserted into and pulled outfrom the gate, wherein the cavity includes a cylindrical mold cavity anda columnar core to be coaxially inserted into and pulled out from themold cavity, and the gate for injecting molding material is formed inalignment with the center axis of the mold cavity, wherein the core hasa cone-shaped front end portion, and when the core is inserted into themold cavity, the front end portion of the core is inserted into thegate, and a gap of an identical width is formed all around the peripherybetween the core and the gate, wherein, when the valve pin is partedfrom the gate, the molding material flows uniformly into the cavity allaround the periphery thereof from the gap, wherein the valve pin isformed with circular cone recesses on the end face at the cavity side,and a communicating hole communicating the circular cone recess and themolding material injection path is formed, wherein, when the valve pinfit with the gate to perform gate-cut, the cone-shaped front end portionof the core fits with the circular cone recess of the valve pin, andsurplus molding material caught between the circular cone recess and thefront end portion can escape to the molding material injection paththrough the communicating hole.
 3. The metal mold according to claim 2,wherein the mold cavity is for forming the outer surface of a cylinderand the core is for forming the cylinder inner surface.
 4. (canceled) 5.A formed body molding method, comprising the steps of: (a) injecting ametered molding material from the molding material supply side into acavity via a gate to fill the cavity therewith, (b) after filling thecavity, applying and maintaining a predetermined pressure to the moldingmaterial within the cavity, (c) after completing the pressure applyingand maintaining step, cutting off the gate, (d) cooling the moldingmaterial within the cavity to solidify into a molding, and then (e)taking out the molding, wherein the cavity includes a cylindrical moldcavity and a columnar core to be coaxially inserted into and pulled outfrom the mold cavity, and the gate for injecting molding material isformed in alignment with the center axis of the mold cavity, the moldingmaterial is injected from the front end side of the core to fill themold cavity therewith, the core has a cone-shaped front end portion, inthe step (a), the front end portion of the core is inserted into thegate, a gap of uniform width is formed all around the periphery betweenthe gate and the core, and the molding material flows uniformly into allaround the periphery of the cavity from the gap, in the step (c), whenthe valve pin disposed so as to be inserted into and pulled out from thegate at the supply side of the molding material is inserted into thegate to perform gate-cut, and when the cone-shaped front end portion ofthe core is inserted into a circular cone recess formed on the end faceof the cavity of the valve pin, inescapable surplus molding materialcaught between the circular cone recess and the front end portion canescape to the molding material supply side through the communicatinghole.
 6. The formed body molding method according to claim 5, whereinthe mold cavity is for forming the outer surface of a cylinder and thecore is for forming the cylinder inner surface.
 7. (canceled) 8.(canceled)